Adding secondary textures to models?

I have little-to-no experience with 3dsmax and zmodeler, most of my experience lies in Photoshop. That being said, I've done plenty of texture edits for GTA V, but I'd like to take it one step further. I want to edit one of the biker cuts to have another, secondary texture overlaying the base one. It's practically impossible to do a half-decent retexture in order to put some custom patches and pins on it. Would it be possible to somewhat "paint" a separate normal and bump map with a different layout than the original texture onto the original model, while still utilizing the original texture?